Various kinds of colored images are formed on substrates. For example, color filter may be formed by providing each picture element with a colorant so as to selectively transmit each of the three primary colors, namely, red, green and blue. To provide such picture elements having colorants, techniques including dyeing, printing, electrodeposition and pigment dispersion have come into practical use.
The dyeing method is disadvantageous because it is complicated and expensive when carried out in a manufacturing environment. In this method, a photosensitive solution is applied to a substrate followed by treating with a certain dye (Photopolymer Technology, edited by Yamaoka and Nagamatsu, Nikkan Kogyo shinbun-sha, 1988, pp. 504-513). The printing method is troublesome with respect to surface evenness of layers comprising printed transparent coloring picture elements, correctness of printed pattern shapes, precision of fixing pattern positions, etc. The electrodeposition method is disadvantageous because it requires previous formation of an electrode on a transparent substrate. As a result, there is little freedom in arranging the picture elements.
The pigment dispersion method provides excellent manufacturing stability. The process of the pigment dispersion method consists of dispersing a pigment into a photopolymer, applying the dispersion thus prepared to the substrate, pattern exposing the photopolymer layer thus prepared to light, and developing to form a monocolor picture element pattern. Picture element patterns for a color filter containing a plurality of colors are formed on a substrate by repeating the process many times. However, the picture element pattern tends to reduce light transmission. This is because the pigment particles that are dispersed into the polymer as colorants scatter and absorb light. Furthermore, scattering and double refraction of light by the pigment particles cause the axes of polarization to rotate, thereby resulting in a reduced contrast ratio of liquid crystal displays (The 7th Colorific Optics Conference, 1990, 512 Color Display 10.4 "Color Filters for Size TFT-LCD", by Ueki, Ozeki, Fukunaga, and Yamanaka).
On the other hand, the pigments that can be used for this purpose are limited to some extent because of the characteristics thereof such as dispersion properties. Consequently, color correction must be carried out to obtain the desired chromaticity. As a simple method, it is common practice to simultaneously use a yellow or purple pigment for color correction. However, the use of a yellow pigment considerably increases the above-described light scattering and absorption.
A known method which has been proposed to solve the above-noted problem inherent in pigments is to use dyes in place of the pigments [JP-A-57-16407 (The term "JP-A"as used herein means as an "unexamined published Japanese patent application"), JP-A-61-94004, JP-A-61-15106, JP-A-63-129322 and JP-A-63-298304, and U.S. Pat. Nos. 4,818,075 and 4,877,697]. However, in general, dyes disadvantageously have less durability as compared to pigments. Despite this, JP-A-6-9891 describes that quinophthalone dyes are durable, and that a resin dissolved in an organic solvent together with the dyes is applied to a substrate to form a film. However, to prepare a multicolor image in a similar manner, the respective solutions containing different organic solvent-soluble dyes must be repeatedly applied to a substrate. This causes the dyes to ooze out of previously formed picture elements such that desired chromaticity is not obtained.